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You are here: MacNN Forums > Hardware - Troubleshooting and Discussion > Mac Notebooks > The ambiguity of 1 gb matched vs 1.25 gb unmatched

The ambiguity of 1 gb matched vs 1.25 gb unmatched
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p0stman
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Sep 23, 2006, 01:48 AM
 
I guess the question is always 2 x 512 VS. 1 x 1 gb + 256 mb. I have been looking for the answer to that as well. Unfortunately and surprisingly, no one has done a test with the precise setup mentioned. The best answer I have received is from a friend doing a masters in computer science and he tells me 1.25 gb will outperform a 1 gb matched and its benefits in just about every respect.

Also, I guess the forums are really not a good place to ask about something like this, as most posters mix-match information from different sources or basically make an educated "guess" to find the best estimate. In this case for example, while people are aware that having matched pairs bring a small benefit, what is needed is a compasion. When we take into account that we don't exactly know how much more performance a 256 mb gain is as well, the question of 1 gb matched vs 1.25 unmatched becomes ambiguous. In this case the best decision that can be made is to go with 1.25, since at the very least this offers the option of sensably upgrading to 2 gb later, where the ambiguity ends (hence most people get 2 gb to stop their worrying.)

The general concensus in going with the 1.25 gb is always influenced by the assumption that it will sooner or later be upgraded to 2 gb, not necessarily the benefits vs. 1 gb matched.
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p0stman  (op)
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Sep 23, 2006, 02:35 AM
 
I also find it kind of odd when people (and also "experts") claim that having 1.25 gb (unmatched) vs 1 gb (matched) or even 2 gb (matched) vs 1 gb (matched) will dramatically increase graphic performance (yes, 15-20% is dramatic.)

Also, tests by BearFeats have indicated matched pairs offer over 50% increase in performance for Quake 3, which is VERY perplexing since they were comparing a 512 mb matched VS. a whopping 1.25 gb unmatched.

This is a mystery to me because the Integrated Video RAM only has a capacity of 64 mb. It is bottlednecked at this capacity... so even if one of the cards have only 256 mb it should not make any difference, nor is having 20 gb of matched RAM (considering the RAM requirement for running other aspects of the game is met.)

The only benefit I can see from having 2 huge chunks of matched RAM is from users who utilize the parallel processing system, running XP and OSX at the same time, and for those who run more than 2 highly intensive applications at the same time.

Can someone shed ome light on this?
( Last edited by p0stman; Sep 23, 2006 at 02:46 AM. )
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analogika
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Sep 23, 2006, 07:09 AM
 
The graphics card has no memory of its own; it's "shared" memory.

Meaning it's on the same memory bus as the rest of the computer.

The graphics card requires matched pairing for optimal performance, since it can go into a special symmetric access mode then. If it can't, it slows down the whole memory bus for the entire machine.
     
p0stman  (op)
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Sep 23, 2006, 12:09 PM
 
However, even if the RAM cards do not match in capacity, they're of the same speed - both 667 MHz. The video memory will only take as much as 64 MB, so even if it draws the same amount from both cards, it will never surpass the RAM card with the lowest capacity. However, if it were another case - if the video card shared let's say 600 mb of memory, it could go on to draw 300 mb from each card, and in this case it would superceed the 256 mb card, and it would have to draw additional memory from the larger capacity card.

But in the case of such a small share - 64 mb, it should not make any difference at all.

I have a friend with a black Macbook with 2 x 512 mb memory from apple. I tried running C&C generals and the performance is very similar. It took about the same amount of time getting through the ingame cinematics (which took forever on a 512 mb card.)
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mduell
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Sep 23, 2006, 01:51 PM
 
The better configuration depends on usage.

Playing games? With the integrated graphics/shared memory, higher bandwidth is better even though it means less capacity.

Large numerical simulations? More capacity trumps bandwidth in the majority of cases.
     
p0stman  (op)
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Sep 23, 2006, 02:02 PM
 
The point is that the integrated graphics is capped at 64 mb. That's the maximum you can share with both channels of RAM, so having more RAM or matched pairs does not mean the cap is suddenly 65 mb now.

Apple has a bad habit of unjustifiably commenting on the capabilities/configurations of their hardware and creating masses of confusion within the consumers.
( Last edited by p0stman; Sep 23, 2006 at 02:08 PM. )
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amazing
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Sep 23, 2006, 02:14 PM
 
I think barefeats.com is the only website I've seen do tests on the RAM configuration. Since you're aware of their tests, there's not much to add--it's the only data to base a decision on.

It's more a question of how to use your money strategically: by buying one GB RAM now, you accept the not-quite-optimum RAM restrictions for the short term, knowing that you're saving up the money to eventually buy the 2nd GB RAM chip. You trade off momentary discomfort for later gain. And later on, once you've budgeted and got the balanced optimum RAM configuration, this slight hiccup really won't seem all that crucial.

There's a saying about "having a taste for champagne on a coca-cola budget." That's just life in the world of tech toys.
     
p0stman  (op)
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Sep 23, 2006, 02:31 PM
 
But do you not have to buy perfectly matching RAM? You cant really wait and upgrade several month into the future, or the RAM would not be perfectly identical...

But do the RAM have to be perfectly identically or can it just be same specs... bus speed and memory?
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mduell
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Sep 23, 2006, 02:53 PM
 
Originally Posted by p0stman
The point is that the integrated graphics is capped at 64 mb. That's the maximum you can share with both channels of RAM, so having more RAM or matched pairs does not mean the cap is suddenly 65 mb now.
If I recall correctly, the Intel Macs will dedicate 64MB system RAM to the graphics chip if you have 512MB system RAM, but when you install more memory it allocates more to the graphics chip (GMA950 supports up to 224MB).

Originally Posted by p0stman
But do you not have to buy perfectly matching RAM? You cant really wait and upgrade several month into the future, or the RAM would not be perfectly identical...

But do the RAM have to be perfectly identically or can it just be same specs... bus speed and memory?
All you need to match are the capacity, speed, density/configuration, and latency. You can buy another module in a couple months or even years that matches the one you buy now.
     
p0stman  (op)
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Sep 23, 2006, 07:32 PM
 
Capacity and speed is clearly indicated... but what exactly is meant by configuration and latency?
( Last edited by p0stman; Sep 23, 2006 at 07:56 PM. )
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amazing
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Sep 24, 2006, 12:23 AM
 
You can run unbalanced RAM configs for as long as you want. Somewhere down the road, finances permitting, you add another RAM chip from the same source you bought the first RAM chip. That's about as balanced as life gets.

What impressed me the most, is the article at barefeats.com which showed that the 2.0 MB performed slightly better than the 2.0 MBP at all regular tasks, except for games (because of the GMA 950 handicap.) So, that's what I'd focus on--since I don't play those games--and now I'm only waiting till they offer the MB with a matte screen. There's no way I could tolerate all the reflections in a glossy screen...
     
mduell
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Sep 24, 2006, 01:19 AM
 
Originally Posted by p0stman
Capacity and speed is clearly indicated... but what exactly is meant by configuration and latency?
Configuration is the number of chips on the memory module; density is the size of each chip.
Latency is all the RAS/CAS numbers... sometimes abbreviated as CAS=5 or CL=5, sometimes completely listed as 5-5-5-12 or similar
     
Eug Wanker
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Sep 24, 2006, 01:33 AM
 
On a MacBook with its integrated GMA 950 graphics, it would be ill-advised to get unmatched RAM, unless you never do anything graphics intensive. Remember, integrated graphics is one of the things that can regularly saturate the memory bus, and hence system memory speed is extremely important.


Originally Posted by mduell
If I recall correctly, the Intel Macs will dedicate 64MB system RAM to the graphics chip if you have 512MB system RAM, but when you install more memory it allocates more to the graphics chip (GMA950 supports up to 224MB).
That is incorrect. While the chipset supports that, Apple locks it to 64 MB AFAIK. I think that's stupid, but that's the way it is.
     
p0stman  (op)
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Sep 24, 2006, 05:07 AM
 
So how much RAM do you need to utilize the 224 mb?
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mduell
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Sep 24, 2006, 11:59 AM
 
Originally Posted by Eug Wanker
That is incorrect. While the chipset supports that, Apple locks it to 64 MB AFAIK. I think that's stupid, but that's the way it is.
While most laptops with GMA950 allow you to set the amount of RAM used as VRAM, I've read a few places that the Intel Macs will automatically adjust the VRAM allocation depending on total system RAM... something like 64MB/512MB, 128MB/1GB and 192MB/2GB.

MacWorld's benchmarks have a curious doubling of framerate in Quake3 going from 512MB to 2GB on a MacBook - Macworld: First Look: MacBook gaming: A graphics concern?
     
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Sep 25, 2006, 01:51 PM
 
Originally Posted by amazing
It's more a question of how to use your money strategically: by buying one GB RAM now, you accept the not-quite-optimum RAM restrictions for the short term, knowing that you're saving up the money to eventually buy the 2nd GB RAM chip. You trade off momentary discomfort for later gain. And later on, once you've budgeted and got the balanced optimum RAM configuration, this slight hiccup really won't seem all that crucial.
     
tleeds
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Oct 4, 2006, 11:23 PM
 
The reason a matched pair increases graphics performance over an unmatched pair is because when you have a matched pair of memory sticks, the memory controller goes into dual channel mode which increases the available memory bandwidth by 2x. A commonly held misconception with graphics is that the size of the video ram is more important than the speed of the video ram. Think of it this way, The amount of video ram is like a bathtub you're trying to drain. With an unmatched stick, you can only drain it with a 1" pipe. No matter how big the bathtub is, you'll still only be able to fit so much data through that pipe. Pairing the sticks lets you use a 2" pipe to drain the tub. To (needlessly) continue the metafore, the bathtub is filled with graphics textures. The amount of textures you can fit in the tub has very little to do with how fast you can get them out (and in) to the tub. The 1280x800 display on the Macbook and limited performance (no 8-16xAA and AF) of the GMA950 mean more than 64MB of video memory is nearly useless. That extra memory will do alot more good powering OS-X's memory hungry kernel.

Read any graphics review online and you'll notice that cards where the only difference is the memory size will perform at exactly the same speed right up until you reach super high resolutions (At this point, the lower end card starts swapping textures to main memory and takes a performance hit). For the previously stated reasons, this is unlikely to occur on a Macbook with built in graphics.

/End Graphics 101
     
analogika
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Oct 5, 2006, 03:19 AM
 
at the bathtub metaphor.

Thanks for the image - that's a good one to explain the architecture.
     
Eug Wanker
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Oct 5, 2006, 01:55 PM
 
Originally Posted by mduell
While most laptops with GMA950 allow you to set the amount of RAM used as VRAM, I've read a few places that the Intel Macs will automatically adjust the VRAM allocation depending on total system RAM... something like 64MB/512MB, 128MB/1GB and 192MB/2GB.
I have 2 GB RAM, and 64 MB video RAM is listed in the Apple System Profiler.
     
drnkn_stylz
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Oct 6, 2006, 11:39 AM
 
So the GMA950 is an integrated card with 64mb of memory, and since it is integrated, that means it will "borrow" more memory from system RAM, when a program (such as a game) need more than the 64mb supplied. Correct?

Now, Eug Wanker states that Apple "locks" the card so it cannot use more than the 64mb. Doesn't this make its integration pointless? How is it locked? Also, if it has been locked, there must be a way to unlock it. How could someone go about doing this?
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Eug Wanker
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Oct 7, 2006, 12:59 AM
 
Originally Posted by drnkn_stylz
So the GMA950 is an integrated card with 64mb of memory, and since it is integrated, that means it will "borrow" more memory from system RAM, when a program (such as a game) need more than the 64mb supplied. Correct?
Not according to the Apple System Profiler. No matter how much stuff is loaded, it's always at 64 MB. I cannot vouch for its accuracy however.

Now, Eug Wanker states that Apple "locks" the card so it cannot use more than the 64mb. Doesn't this make its integration pointless?
No. The point of integration is low cost.
     
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Oct 7, 2006, 07:19 AM
 
Originally Posted by tleeds
The reason a matched pair increases graphics performance over an unmatched pair is because when you have a matched pair of memory sticks, the memory controller goes into dual channel mode which increases the available memory bandwidth by 2x. A commonly held misconception with graphics is that the size of the video ram is more important than the speed of the video ram. Think of it this way, The amount of video ram is like a bathtub you're trying to drain. With an unmatched stick, you can only drain it with a 1" pipe. No matter how big the bathtub is, you'll still only be able to fit so much data through that pipe. Pairing the sticks lets you use a 2" pipe to drain the tub. To (needlessly) continue the metafore, the bathtub is filled with graphics textures. The amount of textures you can fit in the tub has very little to do with how fast you can get them out (and in) to the tub. The 1280x800 display on the Macbook and limited performance (no 8-16xAA and AF) of the GMA950 mean more than 64MB of video memory is nearly useless. That extra memory will do alot more good powering OS-X's memory hungry kernel.

Read any graphics review online and you'll notice that cards where the only difference is the memory size will perform at exactly the same speed right up until you reach super high resolutions (At this point, the lower end card starts swapping textures to main memory and takes a performance hit). For the previously stated reasons, this is unlikely to occur on a Macbook with built in graphics.

/End Graphics 101
But a 2" pipe is 4 times the section as a 1" pipe!

I like the bathtub metaphor too

When you say that more RAM will fight OSX hunger, you mean it will give less beachballs?
     
drnkn_stylz
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Oct 8, 2006, 04:08 PM
 
I HATE beachballs!
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p0stman  (op)
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Oct 8, 2006, 07:32 PM
 
Acctually, it will help if you acctually run out of memory. If you never utilize the memory there is nothing more RAM can do about beachballs.
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